Review of mechanical degradation and de-aggregation of drag reducing polymers in turbulent flows

The efficiency of drag reduction (DR) is known to be impaired by mechanical scission of molecules, which is a great obstacle to the practical use of flexible polymeric drag reducers. In this review, I try to give an account of the main aspects of this problem, pointing to the important variables (concentration, molecular weight, temperature, Reynolds number, quality of solvent, residence time, and relaxation time) that accelerate or delay the molecular scission of linear polymer chains in turbulent flows. The impairment of DR can also be related to de-aggregation, owing to the rupture of the intermolecular associations, instead of intra-molecular mechanical scission.